N900 and 4-bay external USB drive

I used medisonic HFS-SU32S 4 bay 3.0 USB from amazon and it read all four of my drive fine. I had a problem at first; I moved drive around in bay, and then deleted file that created by WD N900 after I move it around on storage, then click rebuild button on webpage. But before that, I installed WD quick view. Hope that help. I have a problem accessing FTP outside my home network. Can anyone help?